First Strike Ultra Spherical Projectiles USP 100 Count .50 Caliber Blue Clear Shell White Powder FillThe First Strike . 50 Caliber Ultra Sphere Projectiles (USP) are a great addition to the First Strike projectile family. The First Strike USP balls are powder filled perfectly round projectiles that deliver what standard gelatin paintballs cannot; consistent, dimple free accuracy. The weather proof polystyrene shell ensures consistent performance in even the most inclement weather and can even endure the heavy spring pressure required in todays magfed